Ni-Mn Alloys Research Articles

Rotational magnetic properties of Ni-Mn and Au-Fe spin-glass alloys.

Magnetization-vector measurements were performed on field-cooled polycrystalline disks of ${\mathrm{Ni}}_{75}$${\mathrm{Mn}}_{25}$ and ${\mathrm{Au}}_{85}$${\mathrm{Fe}}_{15}$ rotated in a stationary field H. For ${\mathrm{Ni}}_{75}$${\mathrm{Mn}}_{25}$ at 4.2 and 10 K, it is found that the induced anisotropy, which rotates rigidly with the sample for all H, is predominantly unidirectional but with uniaxial and higher-order components that are not negligible. Moreover, the rotational magnetization Mp/${\mathrm{r}}_{\mathit{r}\mathit{o}\mathit{t}}$ is seen to be a unique function of the total effective field Hi/${\mathrm{r}}_{\mathit{e}\mathit{f}\mathit{f}}$ composed vectorially of H plus the anisotropy field ${\mathbf{H}}_{\mathit{K}}$, where M /${\mathrm{r}}_{\mathit{r}\mathit{o}\mathit{t}}$ extends from its saturation value down to zero at Hd/${\mathrm{r}}_{\mathit{e}\mathit{f}\mathit{f}}$=0. For ${\mathrm{Ni}}_{75}$${\mathrm{Mn}}_{25}$ at higher temperatures, it is found that for H above a threshold value the direction of ${\mathbf{H}}_{\mathit{K}}$ changes relative to the rotating sample. This phenomenon is also observed in ${\mathrm{Au}}_{85}$${\mathrm{Fe}}_{15}$ at 4.2 K, and the directional changes of ${\mathbf{H}}_{\mathit{K}}$ are seen to be a dissipative process, which is macroscopically frictional. Qualitative comparisons are made with the available theory.

An analysis of short-range order in Ni3Mn alloy by means of electrical resistivity measurements

The general task of the present work is to test the correlation between experimental resistivity and atomic ordering in alloys. The authors used the Rossiter model to describe the SRO contribution to the total electrical resistivity. This model allows them to calculate the SRO resistivity at a given temperature as long as the Cowley-Warren parameters are known. The theory of Clapp and Moss (1966) has been applied to obtain the Cowley-Warren parameters as functions of temperature and interaction energies of atoms at different distances. Hence, the SRO resistivity could, like the Cowley-Warren parameters, be represented as a function of interaction energies and temperature. To test this model the authors used experimental resistivity data for Ni3Mn, and from the total resistivity they obtained the SRO contribution, to which they fitted the model function. From the above calculations the authors got the values of interaction energies, from which they could obtain the temperature dependencies of the Cowley-Warren parameters.

Spin dynamics in a homogeneous Mn(38% Ni) alloy

Inelastic neutron scattering measurements performed for Mn(38% Ni) alloy yielded the following values of the spin wave spectrum: the velocity v = 140 ± 20 meV A ̊ and the energy gap E g ⋍ 3.5 meV . A considerable reduction of the SW lifetimes was observed. The SW parameters in Mn-Ni alloys are compared to those obtained for the Mn-Fe system.

Magnetic resonance study and computer simulation for the induced unidirectional anisotropy of reentrant Ni-Mn alloys.

Microwave resonance studies are reported on the ${\mathrm{Ni}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$ (x=0.230 and x=0.255) alloys in the temperature range 4.2--300 K. By fitting the resonance lines to the solutions of the Landau-Lifshitz equation for the metallic ferromagnetic systems and considering both parallel and perpendicular magnetization for the thin disklike specimen, we have obtained the macroscopic anisotropy ${H}_{A}^{\mathcal{'}}$ and linewidths \ensuremath{\Delta}H, as a function of temperature for both the zero-field cooling and field cooling cases. We conclude that the main contribution to the anisotropy comes from Dzyaloshinsky-Moriya--type interaction between the frustrated spins within the domains, while the contribution of the spins in the domain walls is negligible. We also confirm that the induced anisotropy can be rotated elastically by the internal effective field.

Direct evidence for triple-Q spin-density wave in fcc antiferromagnetic Mn-Ni alloy.

It is shown by a brief calculation that the method of anisotropy measurement of $\ensuremath{\gamma}$-ray emission from spin-polarized nuclei is a useful tool to investigate multiple-spin-modulation waves which have been suggested to exist in several kinds of materials but have not yet been proven by definitive experimental evidence. An application of this method is made for a fcc antiferromagnetic Mn-Ni alloy and the first direct experimental evidence for a triple-Q spin-density wave is given.

Electronic structure and kinetic properties of NiMn and NiTi alloys

The electrical resistivity (ρ) of the alloys NiMn and NiTi in the B2-phase is calculated from first principles. The electronic structure is calculated by the MH CLV method. Phonon dispersion curves are obtained in the Born-Karman model of mechanical atomic constants with allowance for the interaction of nearest neighbors. The effective thermal and optical electron masses are calculated for each sheet of the Fermi surface of NiMn. An analysis is made of the connection between the electronic structure and electrical resistivity of alloys NiMn and NiTi. Satisfactory agreement is obtained between calculated temperature dependences ρ(T) and experimental data.

Measurement and modeling of Alloy-Spinel-Corundum equilibrium in the Ni-Mn-Al-0 system at 1873 K

The oxygen content of liquid Ni-Mn alloy equilibrated with spinel solid solution, (Ni,Mn)O. (1 +x)A12O3, and α-Al2O3 has been measured by suction sampling and inert gas fusion analysis. The corresponding oxygen potential of the three-phase system has been determined with a solid state cell incorporating (Y2O3)ThO2 as the solid electrolyte and Cr + Cr2O3 as the reference electrode. The equilibrium composition of the spinel phase formed at the interface of the alloy and alumina crucible was obtained using EPMA. The experimental data are compared with a thermodynamic model based on the free energies of formation of end-member spinels, free energy of solution of oxygen in liquid nickel, interaction parameters, and the activities in liquid Ni-Mn alloy and spinel solid solution. Mixing properties of the spinel solid solution are derived from a cation distribution model. The computational results agree with the experimental data on oxygen concentration, potential, and composition of the spinel phase.

Magnetic anisotropy induced by magnetic field cooling in Ni3Mn alloys

The magnetic anisotropy of Ni3Mn alloys with various degrees of atomic order has been investigated by a torque magnetometry. By cooling down from 300 to 80 K in a magnetic field of 10 kOe, a unidirectional anisotropy Kd with a period of 360° was induced. The temperature dependence of this anisotropy can be expressed by exp(Q/T) from 50 to 20 K and by log(T) below 20 K. The magnitude of Kd was increased by a factor of 100 during cooling down from 50 to 4.2 K. Furthermore, the hysteresis loop at 4.2 K for a disordered alloy was shifted such that the easy direction of magnetization is that of the cooling magnetic field. They are discussed in terms of exchange anisotropy and the size distribution of clusters with antiferromagnetic coupling.

CURIE-TEMPERATURE "SLATER-PAULING CURVE"

The systematic variation of the Curie-temperature Slater-Pauling curve has been explained for the first time on the basis of the finite-temperature theory of the local environment effect. The peculiarity of the Curie temperatures in Fe-V, Fe-Ni, and Ni-Mn alloys is elucidated by using the effective exchange couplings.

Pressure Effects Estimated from Forced Volume Magnetostriction for Ni–Tm [Tm=Ti, V, Cr, Mn] Alloys

Pressure effects on magnetic moment µ and Curie temperature T c have been estimated indirectly from forced volume magnetostriction dω/d H measured by 3-terminal capacitance method instead of strain gauge technique for Ni–Tm [Tm=Ti, V, Cr, Mn] alloys. The relation between pressure coefficients, d ln µ/d p and d ln T c /d p , are analyzed according to Inoue-Shimizu discussion. The values of the coefficient C /χ hf T c obtained seem to decrease gradually to about 1 in the limit of weak itinerant ferromagnet with decreasing T c toward 0 K for Ni–Tm [Tm=Ti, V, Cr] alloys except for Ni–Mn alloys.

NMR study of re-entrant spin-glass state in NiMn alloys

The temperature dependence of the average hyperfine field H̄ i and the nuclear spin-lattice relaxation time T 1 of 55Mn on three different types ( i = I, II and III) of Mn atoms in NiMn alloys containing 10 and 15 at % Mn have been measured. In 15 at % Mn alloy, H̄ III associated with Mn atoms having an antiparallel moment μ III increases abruptly at 12K, while H̄ I and H̄ II associated with Mn atoms having parallel moments μ I and μ II do not with decreasing temperature. On the other hand T −1 1 of 55Mn of all three types of Mn atoms are largely enhanced at the same temperature, 12 K. This behavior was not observed in 10 at % Mn alloy. These effects observed in 15 at % Mn alloy are considered to be due to the freezing of the transverse component of the antiparallel moment μ III due to the onset of the re-entrant spin-glass transition at 12 K.

Neutron irradiation of FeMn, FeCrMn and FeCrNi alloys and an explanation of their differences in swelling behavior

The swelling and phase stability of neutron-irradiated FeCrMn and FeCrNi alloys are compared in the range 420–600°C. While the behavior of the two alloy systems exhibits many similarities, that of the FeCrMn system is more complex, involving a higher level of phase instabilities. However, the sensitivity of radiation-induced density changes to composition is less in the FeCrMn system. In the FeCrMn system there are three major components of density change, namely void growth, ferrite formation and lattice parameter changes of the retained austenite; whereas void swelling is the only major component of density change in the FeCrNi system.

Spin waves in itinerant multiple-spin-density-wave systems. II

For pt.I see ibid., vol.17, no.5, p.1175 (1987). The spin wave energies and widths for linear- (LSDW) and multiple-spin-density-wave (MSDW) systems are calculated using the formalism developed in pt.I for an itinerant model. Calculations were made for the wave-vector q parallel and perpendicular to the magnetisation in the LSDW state; the velocities near the zone centre were found to depend on the direction of approach to the zone centre and the widths appear to be linear in q for the parallel case but non-linear in the perpendicular case. Three acoustic branches were found for the triple-spin-density-wave case. The widths for these were found to be linear in q. There is a fourth spin wave that plays a vital role in transitions from one MSDW state to another. The authors discuss the nature of these spin-orientation phase transitions and how they can be recognised in the inelastic scattering cross section. The softening of the shear elastic constant is shown to be consistent with the onset of such transitions. Finally, it is conjectured that the orthorhombic phase in the Mn-Ni alloy phase diagram may be accounted for by a MSDW state.

Magnetoresistance and magnetic susceptibility of hydrides of disordered Ni-Mn alloys

Magnetoresistance and magnetic susceptibility of hydrides of disordered Ni-Mn alloys

Satellite hyperfine fields in low concentration NiMn alloys

Concentration- and temperature dependent measurements were made on NiMn-alloys with the perturbed angular correlation technique (PAC). At room-temperature, samples of 1.3; 2.4; 3.6; 5.6; 6.9 and 8.3 at%Mn were examined. Field values on both sides of the Ni-value were observed with a pronounced concentration dependence above 3 at%Mn. The 3.6 at%Mn-sample was examined as function of temperature between 284 K and 573 K. Each of the fields has the same temperature-behaviour, resulting in the same Curie-temperature, which is however smaller than the Curie-temperature for pure Ni.

Furnace for rapid change of temperature for neutron diffraction

A new furnace for neutron diffraction experiments is capable of heating and cooling a sample very rapidly. The rapid heating is done by two circular infrared lamps placed over and under a sample, whose radiation is roughly focused on the sample by a reflector. The rapid cooling is done by high-pressure gas blows against the sample from two circular nozzles which are also placed over and under the sample. This system enables us to obtain the heating rate of over 1000°C/min and cooling rate of −500°C/min for an alloy of 10 mm diameter and 30 mm length. The performance is sufficient to carry out some kinetics measurements in real-time neutron diffraction by the use of a position-sensitive detector. This kind of experiment is demonstrated by the observation of the relaxation process of order–disorder transitions in CuZn and Ni3Mn alloys.

X-ray emission spectra and electronic structure of Mn impurities in diluted Al, Ni and Cu-based solid solutions

Mn Lα emission spectra of pure metal and AlMn, CuMn and NiMn alloys are presented. For CuMn and NiMn alloys, the dependence of the width of structureless emission band on Mn concentration is discussed. For Al0.995Mn0.005 alloy, distoted shape of the emission spectrum reveals the spin splitting of impurity virtual bound states.

Small angle neutron scattering from disordered [formula omitted]-Mn alloys

Neutron small angle scattering measurements on disordered Ni Mn alloys containing 21.8, 23.8,24.8 and 26.3 at% Mn are reported. There is a marked increase in the small angle neutron scattering intensity with decreasing temperature for all the alloys. For the 21.8 at% Mn alloy there is a re-entrant phase which occurs at approximately 100 K but the lineshape of the scattering shows departures away from a Lorentzian at small wavevectors, as has been previously reported in the literature. For the alloys around the critical composition of 25 at% Mn there is an uninterrupted rise in the small angle scattering with temperature. The lineshape of the 23.8 at% Mn alloy also shows some signs of a departure from a Lorentzian. For the remaining alloys the temperature dependence of the inverse correlation length shows the steady evolution of long wavelength magnetic correlations down to 5 K. This is also reflected in the temperature dependence of the extrapolated small angle intensity to Q = 0 which gives a measure of the bulk static susceptibility and is in some agreement with previously reported magnetization and neutron scattering measurements.

Transformation behavior of nearly stoichiometric Ni-Mn alloys

The transformation behavior of Ni-Mn alloys in the vicinity of the stoichiometric composition has been studied using transmission electron microscopy, X-ray diffraction, optical microscopy, and electrical resistivity measurements. The transformation behavior was found to be markedly different in Mn-rich alloys and Ni-rich alloys. In Mn-rich alloys a martensitic transformation between L20 (B2) and L10 structures takes place, which possesses many features common to alloys exhibiting a thermoelastic martensitic transformation. On the other hand, in Ni-rich alloys an order-disorder transformation between A2 and L10 structures occurs. The martensitic transformation features {111} transformation twins as the transformation substructure while the ordering reaction involves {101} order twins. In the Mn-rich alloys, the martensitic phase, if either slowly cooled or annealed at intermediate temperatures, becomes “tempered”, resulting in a noncrystallographic, essentially featureless microstructure apart from the presence of occasional {111} twins.

Electron microscopic study ofθ-phase martensite in Ni-Mn alloys

Electron microscopic observations have been made onθ-phase Ni-Mn martensites which form in nearly stoichiometric Ni-Mn alloys. Three fundamental variant-variant pairs, the “A/B”, “A/C”, and “A/D” types, have been identified as well as other combinations of variants with the aid of crystallographic information given by the phenomenological theory of martensitic transformations. The complex mixing of variants, the abundant presence of dislocations, and the large twinning shear have been pointed out as main crystallographic factors hindering the shape-memory-type deformation in this alloy system, in addition to weak grain boundaries. A new grouping of martensite variants is suggested which as a group cancels the shape strain as well as that found in the normal fundamental plate groups. The new grouping also gives the proper combination of variants for which the intersection becomes a single crystal.